This invention relates generally to a commercial gas convection oven, and more particularly, to a bifurcated tubular heat exchanger which can be positioned within a limited width combustion chamber preferably formed within the heating chamber of such an oven to form a highly efficient convection oven within a limited amount of space.
In convection ovens, food is placed into a heating chamber to be thawed, fried, baked or otherwise cooked or processed by means of the application of heat. Food is processed within the heating chamber by moving heated air along a circulatory path which is defined to provide a selected and controllable temperature of substantial uniformity throughout the heating chamber. The circulatory path is generally defined by the interior walls of the heating chamber, by food supporting racks and possibly by baffling within the heating chamber when the chamber is empty. The air is moved around the circulatory path by means of a fan or blower which is positioned within the circulatory path and usually housed within a separate chamber adjacent to the heating chamber.
The circulated air in convection ovens has been heated by passage over and around electrically heated coils, steam pipes, heated flues or tubular heat exchangers which rely exclusively upon an exchange of heat between the particular heating element utilized and the circulating air to maintain the desired heating temperature in the oven. To increase the efficiency in a gas-fired convection oven, the products of combustion have been introduced directly into the circulating air path of the oven.
For example, in U.S. Pat. No. 4,484,561, a tubular heat exchanger comprises a single spiraling tube having a substantial diameter which passes around a conical central portion of a baffle interconnecting the heating chamber of the oven to an axial air inlet of a blower wheel or fan. The portion of the heat exchanger nearest its inlet end is naturally the most highly heated portion of the heat exchanger. To capitalize on the high heating of the inlet end of the heat exchanger, it has a cross-sectional area which is formed to provide an airfoil type effect for maximum thermal energy transfer to the air. Additional although substantially less heat is extracted from the remainder of the heat exchanger, which comprises approximately 75-88% of the heat exchanger, receives less heat, and transfers that heat to the air with less efficiency due to its relatively large diameter circular cross-section.
To extract still more heat from the gas combustion process for higher efficiency and more rapid heating of the convection oven, the products of combustion are introduced into the circulatory air path of the oven. To enhance the introduction of the products of combustion into the circulatory air path, the outlet of the tubular heat exchanger is positioned in the low pressure inlet of the blower such that the heated products of combustion are drawn into the blower and mixed with the air from the heating chamber. This mixture of air and combustion products is then passed over the heat exchanger to receive additional heat before being directed back into the heating chamber. The convection blower of the oven thus assists a fan which forms a part of and powers a gas burner of the cited prior art patent.
Unfortunately, in the illustrated spiral heat exchanger of the cited prior art patent, maximum heat transfer appears to be limited to no more than approximately 25% of the heat exchanger which also must be of a substantial diameter to accommodate sufficient combustion products to rapidly heat the oven. The large diameter of the spiral heat exchanger tube coupled to the baffle leading to the convection blower dictates that the chamber containing the convection blower be of a substantial dimension relative to the heating chamber of the oven, for example, in the illustrated embodiments, approximately 50%. Further, altering the formation of a portion of the heat exchanger to have an airfoil cross-section adds to the cost of the heat exchanger due to increased fabrication, inventory and assembly costs.
It is, thus, apparent that the need exists for an improved heat exchanger for a gas convection oven which will not only provide rapid and efficient introduction of heat from a gas burner into the circulatory air path of a convection oven, but one which can be constructed inexpensively and will permit compact construction within a limited size convection blower chamber or combustion chamber of a gas convection oven.